Mistakable French : A DICTIONARY OF WORDS & PHRASES EASILY CONFUSED by Philip Thody and Howard Evans (Scribner's: $19.95; 256 pp.) : MERDE! THE REAL FRENCH YOU WERE NEVER TAUGHT AT SCHOOL by "Genevieve," illustrated by Michael Heath (Atheneum: $8.95, paperback; 96 pp.)

S ,s -kicker, tough s ,s bricks--if you can't get along without such words and expressions in English, then you won't want to dispense with them in French either, and in that case "Genevieve" will be your instructor of choice. Broadly speaking (and broadly is how we are speaking), English seems to be richer than French in colorful, metaphorical idioms, but French clearly comes out ahead in morphological abundance. Thus, besides la merde , "Genevieve" lists un emmerdement, un emmerdeur (or une emmerdeuse ), le merdier , un petit merdeux, un demerdeur, la demerde , and the verbs emmerder and demerder in all their handy participial and reflexive forms.

If you tend to delete your expletives before you explete them, however, a more amusing book for you may be Philip Thody and Howard Evans' intriguing compilation of faux amis, "false friends," words whose French meaning you mistakenly think you know because they so resemble English words. Thus isolation in French does not translate our isolation . No, our isolation is translated by their isolement , while their isolation is our insulation .

Some false friends are well-disguised. Against all reasonable expectation, French debonnaire does not translate English debonair ; the French word means relaxed, easy-going but lacks the further English connotation of elegance.

Thody and Evans may have written a book that every translator will want to have on hand; but with their digressive, anecdotal style, they deliver much more than that. Their 10 short chapters are like 10 conversations with a wry, literate friend in a French cafe.

In any of them, a syllable can call for another round of drinks and another half-page of informal enlightenment. The difference between Gaullien and Gaulliste, for example, carries the genial co-authors all the way back to Yalta, from which Charles de Gaulle was notoriously excluded. In today's France, it is Gaullien (in the spirit of De Gaulle), though less than Gaulliste (of the political party founded by De Gaulle), to believe that no French diplomat would ever have been so stupid as the British and the Americans were on that occasion.

Discussing the word libre --ordinarily translated free --Thody and Evans explain that as applied to a French school, the adjective does not mean tuition-free but rather independent , without state sponsorship or support and often, by connotation, Catholic . Their page-long gloss is a capsule history of church-state relations in France.

As for sex, where "Genevieve" offers a checklist of impolite French words for body parts, Thody and Evans explain (among other things) the French expression and custom of cinq a sept , offering as illustration the following sentence from the conservative newsmagazine Le Point: " Aucun journal libre ne peut coucher dans le meme lit que l'Etat, fut-ce entre 5 et 7, " which the co-authors translate with inimitable indirection (after all, they are themselves British): "No independent newspaper can enjoy the favours of the State, even on an intermittent basis."